This specification relates to network communications.
Internet Protocol (IP) communications devices, such as Voice over IP (VoIP) telephones and VoIP call servers enable users to communicate over an IP network. For example, a VoIP call server can receive, from one VoIP telephone, a request to initiate a call with a second VoIP telephone. The request can include, for example, call features that are supported by the VoIP telephone that requested the initiation of the call. The VoIP call server can proceed to set up the call through a negotiation process that use the data included in the request to negotiate the call features for the established call.